This invention relates to rotor assemblies of the type used in rotary machines, such as gas turbine engines, that have rotor blades. More particularly, this invention relates to structure for blocking the flow of gases between the root sections of adjacent rotor blades.
Axial flow gas turbine engines for industrial purposes and for propelling aircraft typically have a compression section, a combustion section and a turbine section disposed about an axis of rotation. An annular flow path for working medium gases extends axially through the sections of the engine. The gases are compressed in the compression section. Energy is added to the gases in the combustion section. The hot working medium gases are expanded through the turbine section.
In the turbine section, the rotor assembly has a rotor disk and rotor blades that extend outwardly from the rotor disk. The rotor blades extend across the flowpath for working medium gases. Each rotor blade has an airfoil which adapts the rotor assembly to interact with the working medium gases. The rotor blades receive work from gases through the airfoils and drive the rotor disk about the axis of rotation.
The rotor disk is adapted by a plurality of axially extending slots to receive the rotor blades. The rotor blades each have a root section which adapts the rotor blade to engage an associated slot in the rotor disk. Tolerance variations between the root section and the axially extending slot under operative conditions allow for a small amount of circumferential movement or “rocking” of the rotor blades in the slot during assembly and under operative conditions. In addition, assembly requirements, tolerance variations and the need to accommodate thermal growth of between the adjacent root sections requires leaving an opening or circumferential gap G between the adjacent root sections. The gap G is in flow communication with the working medium flowpath and provides a leak path for working medium gases to leave the flowpath and leak around the airfoils. This leakage reduces the efficiency of the engine.
In some stages of the rotor section, the rotor blades are cooled to reduce thermal stresses in the rotor blades and to keep the temperature of the rotor blades within acceptable limits. Reducing the stresses and ensuring the temperatures are not excessive provides the rotor blade with a satisfactory structural integrity and fatigue life.
Cooling air is typically flowed for this purpose at a higher pressure than the working medium gases to passages in the root section. The cooling air is then flowed from the root section through other sections of the rotor blade, such as the airfoil and platforms, and discharged into the working medium flow path to provide cooling to the rotor blades. In such cooled rotor blades, the gap G provides a leak path for the cooling air from the root section into the working medium flowpath which also reduces the efficiency of the turbine.
Accordingly, scientists and engineers working under the direction of Applicants' assignee have sought to develop effective sealing constructions for the root sections of rotor blades. One approach to a sealing construction is discussed below with reference to FIG. 4 and FIG. 4A.